In the production of transformers and magnetic cores (such as a saturable core), insulative layers are required between layers of the iron core such that the eddy currents which occur when the core is working under high frequency may be minimized. Conventional process of applying insulative layers comprises painting a polymer-containing insulative coating followed by baking the coating. Since the polymeric constituents of the insulative coating will be scorched if the baking temperature is too high, the thus produced iron core needs not be subjected to further heat-treatment which is necessary for cores made of certain materials (especially amorphous metals) after the insulative layers are applied. Furthermore, baking step will incur further cost.
JP No. 62057677 discloses an insulative thin layer formed on the surface of an amorphous alloy film. An aqueous solution containing mainly lithium silicate is painted on the surface and baked.
JP No. 62056578 discloses a protective layer on the surface of an amorphous alloy strip coated by applying an aqueous treatment liquid containing colloidal alumina hydrate and then firing (baking) the liquid at low temperature of 200.degree. C.
EP No. 0191447 discloses a process of sputtering layers of magnetic and insulative materials to give a tape contact surface of a magnetic head. The insulative materials include MgO, NiO, MgO-MnO, MgO-TiO, SrO-TiO.sub.2, NiO-TiO-MnO, ZnO-Fe.sub.2 O.sub.3. JP No. 61008903 discloses a process to apply a reducing agent containing chromate on the surface of an amorphous alloy thin band. A chemical process was adopted to form an insulative coating on the surface. The metal bands, however, will unavoidably be adversely affected.
U.S. Pat. No. 4,558,297 discloses a process comprising coiling a thin strip of amorphous metal alloy, which is previously heat treated, and interposing an insulative film of organic material between the coiled layers thereof.
JP No. 59211579 discloses a process in which an aqueous acid solution containing chromic acid, phosphoric acid and a fluorine-containing compound is applied on the surface of an amorphous alloy and then baked to form an insulative coating based on chromate and phosphate.
JP No. 59177377 discloses a process in which an alcohol solution of ethyl silicate added with an acid is applied onto the surface of an amorphous alloy and then dried to from an insulative coating layer.
These and other processes of applying insulating layers all involve complex operations. For example, firing or baking is frequently required. Many ingredients are added to ensure homogeneity of the formed insulative layer. The insulated coil or amorphous layers cannot be further heat treated.